Organic light emitting device

ABSTRACT

An organic light emitting device utilizing the micro-cavity effect in the RGB subpixel regions while suppressing the micro-cavity effect in the white subpixel region is provided. The organic light emitting device includes a lower substrate, an anode formed on the lower substrate, an organic emission layer formed on the anode, a cathode formed on the organic emission layer, and a reflection decreasing layer formed on at least a portion of the cathode for reducing reflection of the light emitted from the organic emission layer by the cathode to reduce the micro-cavity effect. Such a selective use of the micro-cavity effect in the organic light emitting device improves the color accuracy, the luminance efficiency and the lifespan of the top emission type organic light emitting device.

TECHNICAL FIELD Cross-Reference to Related Applications

This application is a 35 U.S.C. §371 National Stage Entry ofInternational Application No. PCT/KR2013/011437 filed Dec. 11, 2013,which claims priority to Korean Patent Application Nos. 10-2012-0144928filed Dec. 12, 2012 and 10-2013-0150356 filed Dec. 5, 2013, all of whichare incorporated by reference for all purposes as if fully set forthherein.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an organic light emitting device and amethod of manufacturing the organic light emitting device, inparticular, relates to an organic light emitting device that may enhancepower consumption by improving a light efficiency of an element, andenhance a life span of an element, and a method of manufacturing theorganic light emitting device.

Description of the Related Art

An organic light emitting device is a self light-emitting displaydevice, and may be manufactured to be light and thin since a separatelight source may not be used unlike a liquid crystal display. Inaddition, the organic light emitting device has an advantage in terms ofpower consumption due to a low voltage driving, and is excellent in acolor implementation, a response speed, a viewing angle, and a contrastratio and thus, is being studied as a next generation display.

The organic light emitting device uses color expression schemesincluding a scheme of forming and using an organic light emittingelement that emits red light, green light, and blue light for each pixelregion, and a scheme of forming an organic light emitting element thatemits white light in all pixel regions, and using a color filter.Between the color expression schemes, whereas the scheme of forming andusing an organic light emitting element that emits different colors foreach pixel region has difficulty in a fabrication process, the scheme ofusing a white organic light emitting element and a color filter has anadvantage in terms of productivity, a luminance, power consumption, andthe like and thus, is being widely studied.

SUMMARY OF THE INVENTION

A top emission type organic light emitting display uses asemi-transparent electrode as a cathode to emit light emitted from anorganic emission layer to an upper side. When such a semi-transparentcathode is used, micro-cavity phenomenon naturally occurs in which someportion of light emitted from the organic emission layer is repeatedlyreflected by the cathode and the anode. Depending on the optical lengthbetween the two reflective surfaces, the light of a predeterminedwavelength can be amplified by the constructive interference.

Although the constructive interference of the light can be used toincrease the efficiency of the organic light emitting device, it canalso cause color accuracy problem by shifting the color of the lightemitted from the organic emission layer. For example, in the topemission type white organic light emitting device, some particularwavelength of the white light emitted from the organic emission layercan be amplified. In such a case, the light at the white subpixel regionmay shifted.

Accordingly, the inventors of the invention found that it is difficultto generate desired white light in the white subpixel region, andconceived an organic light emitting device having a new configuration toresolve the difficulty.

Therefore, an object of the invention is to provide an organic lightemitting device capable of enhancing a light efficiency of a device in apixel structure using a red subpixel region, a green subpixel region, ablue subpixel region, and a white subpixel region, and a method ofmanufacturing the organic light emitting device.

Another object of the invention is to provide an organic light emittingdevice capable of enhancing power consumption of a device by improving alight efficiency of an element, and enhancing a life span of an element,and a method of manufacturing the organic light emitting device.

Still another object of the invention is to provide an organic lightemitting device to emit desired white light in a white subpixel regionwhen an RGBW pixel structure is applied to a top emission type organiclight emitting device, and a method of manufacturing the organic lightemitting device.

Objects of the invention are not limited to the objects mentioned above,and other objects not mentioned may be clearly understood by a personskilled in the art from description below.

Accordingly, an aspect of the present disclosure relates to an organiclight emitting device having red, green, blue and white subpixel regionswith a reflection decreasing layer configured to decrease the lightemitted from an organic emission layer by a cathode. In the organiclight emitting device, the anode, the organic emission layer, and thecathode are formed on a lower substrate in the stated order. Thereflection decreasing layer is formed on a part of the cathodecorresponding to the white subpixel of the organic light emittingdevice. The reflection decreasing layer is configured to reduce thereflection of the light from the organic light emission layer by thecathode in the white subpixel region, thereby reducing the occurrencesof the micro-cavity effect in the white subpixel region. The reflectiondecreasing layer can be disposed on the lower surface, the uppersurface, or both the lower and upper surfaces of the cathodecorresponding to the white subpixel region.

In an embodiment, the thickness of the anode in the red subpixel region,the green subpixel region and the blue subpixel region may be differentso that the optical length between the anode and the cathode isdifferent in the red, green and blue subpixel regions. For instance, thethickness of the anode in the red subpixel region can be a predeterminedthickness to define the ideal optical length between the anode and thecathode that causes the micro-cavity effect and amplify a specificwavelength that will pass through the red color filter with minimalfiltration. The improved color accuracy and luminance efficiency of theorganic light emitting device, in turn, results in the improved powerefficiency and the life span of the organic light emitting device.

In an embodiment, an organic light emitting device having a cathode withat least two parts each having different light transmittance rate isprovided. The organic light emitting device includes a first electrodedisposed on a lower substrate. The first electrode may serve as an anodefor the organic light emitting device. An organic emission layer isdisposed on the first electrode. Further included in the organic lightemitting device is second and third electrodes disposed on the first andsecond part of the organic light emission layer, respectively. Thesecond and third electrodes may be electrically connected to each otherand collectively serve as a cathode for the organic light emittingdevice. The second electrode and the third electrode have differentlight transmittances.

In an embodiment, the second electrode and the third electrode areformed so that a light transmittance rate of the third electrode isgreater than a light transmittance rate of the second electrode. Thefirst part of the organic emission layer may corresponds to the red,green and blue subpixel regions, while the second part of the organicemission layer may corresponds to the white subpixel region or theorganic light emitting device. The third electrode with higher lighttransmittance rate than the second electrode creates less micro-cavityeffect in the white subpixel region, thereby allowing accurate whitelight is emitted in the white subpixel region.

In an aspect, there is provided a method of manufacturing an organiclight emitting device with a reflection decreasing layer configured todecrease the light emitted from an organic emission layer by a cathode.The method of manufacturing an organic light emitting device includesforming an anode on a lower substrate, forming an organic emission layeron the anode, and forming a cathode and a reflection reduction layer onthe organic emission layer. In an embodiment, the first reflectionreduction layer is formed on the organic emission layer corresponding tothe white subpixel area of the organic light emitting device, and thecathode is formed over the organic emission layer and the reflectiondecreasing layer. In an embodiment, a second reflection decreasing layeris further disposed on the cathode corresponding to the white subpixelarea of the organic light emitting device. Also, in an embodiment, thecathode is formed on the organic emission layer, and the reflectiondecreasing layer is disposed on the part of the cathode corresponding tothe white subpixel area of the organic light emitting device.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1a is a cross-sectional view of a top emission type organic lightemitting display including a cathode and a reflection decreasing layeraccording to embodiments of the invention;

FIGS. 1b to 1f are conceptual diagrams illustrating various positionsand thicknesses of a reflection decreasing layer of the organic lightemitting display illustrated in FIG. 1 a;

FIGS. 2a and 2b are graphs illustrating a light transmittance of anorganic light emitting display according to various embodiments of theinvention;

FIG. 3a is a cross-sectional view of a top emission type organic lightemitting display including a cathode that includes a plurality ofelectrodes according to embodiments of the invention;

FIG. 3b is a conceptual diagram describing the organic light emittingdisplay illustrated in FIG. 3a ; and

FIG. 4 is a flowchart illustrating a method of manufacturing the organiclight emitting display according to embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Various advantages and features of the present invention and methodsaccomplishing thereof will become apparent from the followingdescription of embodiments with reference to the accompanying drawings.However, the present invention is not limited to exemplary embodimentdisclosed herein but will be implemented in various forms. The exemplaryembodiments are provided by way of example only so that a person ofordinary skilled in the art can fully understand the disclosures of thepresent invention and the scope of the present invention. Therefore, thepresent invention will be defined only by the scope of the appendedclaims.

Indicating that elements or layers are “on” other elements or layersinclude both a case in which the corresponding elements are just aboveother elements and a case in which the corresponding elements areintervened with other layers or elements.

In this specification, like numbers refer to like elements throughoutthe description of the drawings.

Although first, second, and the like are used in order to describevarious components, the components are not limited by the terms. Theabove terms are used only to discriminate one component from the othercomponent. Therefore, a first component mentioned below may be a secondcomponent within the technical spirit of the present invention.

In the drawings, size and thickness of each element are arbitrarilyillustrated for convenience of description, and the present invention isnot necessarily limited to those illustrated in the drawings.

In this specification, an organic light emitting device refers to adevice that emits light having a predetermined wavelength using anorganic emission layer. In this specification, an organic light emittingdisplay corresponds to a case in which the organic light emitting deviceis used for a display. In this specification, the organic light emittingdevice is described as the organic light emitting display forconvenience of description. However, the invention is not limitedthereto, and the organic light emitting display described in thisspecification may be used for lighting.

In this specification, a top emission type organic light emittingdisplay refers to an organic light emitting display in which lightemitted from an organic light emitting element is discharged to a top ofthe organic light emitting display. Light emitted from the organic lightemitting element of the top emission type organic light emitting displayof is discharged toward an upper surface of a substrate on which a thinfilm transistor for driving the organic light emitting display isformed.

Respective features of various exemplary embodiments of the presentinvention can be partially or totally joined or combined with each otherand as sufficiently appreciated by those skilled in the art, variousinterworking or driving can be technologically achieved and therespective exemplary embodiments may be executed independently from eachother or together executed through an association relationship.

Hereinafter, embodiments of the invention are described with referenceto accompanying drawings.

FIG. 1a is a cross-sectional view of a top emission type organic lightemitting display including a cathode and a reflection decreasing layeraccording to embodiments of the invention. Referring to FIG. 1a , anorganic light emitting display 100 includes a lower substrate 110, ananode 150, an organic emission layer 160, and a cathode 170A.

The lower substrate 110 supporting several elements of the organic lightemitting display 100 includes a plurality of subpixel regions. Theplurality of subpixel regions emit different colors, respectively. Theplurality of subpixel regions include a first subpixel region 110Acorresponding to a red subpixel region, a second subpixel region 110Bcorresponding to a green subpixel region, a third subpixel region 110Ccorresponding to a blue subpixel region, and a fourth subpixel region110D corresponding to a white subpixel region. The organic lightemitting display 100 according to embodiments of the invention mayreduce power consumption, and enhance a light efficiency of the organiclight emitting display 100 by employing the fourth subpixel region 110Dcorresponding to a white subpixel region.

A thin film transistor 130 is formed on the lower substrate 110. Thethin film transistor 130 includes an active layer 120, a gate electrode131, a source electrode 132, and a drain electrode 133. The thin filmtransistor 130 is formed for each subpixel region on the lower substrate110, and enables an independent driving for each subpixel region. Inthis specification, the thin film transistor 130 is illustrated amongvarious thin film transistors that may be included in the organic lightemitting display 100 for convenience of description. In addition, inthis specification, the thin film transistor 130 is described as acoplanar thin film transistor. However, an inverted staggered thin filmtransistor may be used.

The active layer 120 is formed on the lower substrate 110. The activelayer 120 includes a channel region 121, and a source region 122 and adrain region 123 disposed on both sides of the channel region 121. Agate insulating film 140 is formed on the active layer 120 to insulatethe active layer 120 from the gate electrode 131. As illustrated in FIG.1a , when the gate insulating film 140 is formed over the entire surfaceof the lower substrate 110, the gate insulating film 140 is formed toinclude a contact hole that opens a portion of the active layer 120, andthe contact hole opens a portion of the source region 122 and the drainregion 123. The gate electrode 131 is formed on the gate insulating film140. An interlayer insulating film 141 is formed on the gate electrode131. The interlayer insulating film 141 is formed to include a contacthole that opens a portion of the active layer 120, and the contact holeopens a portion of the source region 122 and the drain region 123 of theactive layer 120. The source electrode 132 and the drain electrode 133are formed on the interlayer insulating film 141. The source electrode132 and the drain electrode 133 are electrically connected to the sourceregion 122 and the drain region 123 of the active layer 120 through thecontact holes formed in the interlayer insulating film 141 and the gateinsulating film 140, respectively. In order to enhance a light emittingefficiency of an organic light emitting element, a planarization layer142 is formed on the thin film transistor 130 to flatten an upper sideof the lower substrate 110. The planarization layer 142 is formed toinclude a contact hole exposing the drain electrode 133.

An organic light emitting element including the anode 150, the organicemission layer 160, and the cathode 170A is formed on the lowersubstrate 110. The organic light emitting element is driven such that ahole supplied from the anode 150 and an electron supplied from thecathode 170A combine in the organic emission layer 160 to emit light,thereby forming an image. The organic light emitting display 100 is anindependently driven display, and is driven for each subpixel region.Therefore, the thin film transistor 130 and the organic light emittingelement described above are disposed for each subpixel region and thus,the thin film transistor 130 disposed for each subpixel region mayindependently drive the organic light emitting element.

The anode 150 is formed on the planarization layer 142. The anode 150may be connected to the drain electrode 133 of the thin film transistor130 through the contact hole formed in the planarization layer 142. Theanode 150 is formed using a conductive material having a high workfunction to supply a hole, and the anode 150 includes transparentconductive layers 151A, 152A, 153A, and 154A having a high workfunction.

As illustrated in FIG. 1a , when the organic light emitting display 100is the top emission type organic light emitting display, the anode 150includes reflective layers 151B, 152B, 153B, and 154B formed on a lowerside of the transparent conductive layers to discharge light emittedfrom the organic emission layer 150 to an upper side of the organiclight emitting display 100. The reflective layers 151B, 152B, 153B, and154B are formed as conductive layers excellent in a reflectance.

The anode 150 is separately formed for each subpixel region. In thisspecification, the anode 150 formed in a region corresponding to thefirst subpixel region 110A is defined as a first anode 151, the anode150 formed in a region corresponding to the second subpixel region 110Bis defined as a second anode 152, the anode 150 formed in a regioncorresponding to the third subpixel region 110C is defined as a thirdanode 153, and the anode 150 formed in a region corresponding to thefourth subpixel region 110D is defined as a fourth anode 154. Inaddition, as described above, the first anode 151 includes thetransparent conductive layer 151A and the reflective layer 151B, thesecond anode 152 includes the transparent conductive layer 152A and thereflective layer 152B, the third anode 153 includes the transparentconductive layer 153A and the reflective layer 153B, and the fourthanode 154 includes the transparent conductive layer 154A and thereflective layer 154B. A bank layer 145 is formed on the anode 150. Thebank layer 145 is formed to divide adjacent subpixel regions.

The organic emission layer 160 emitting white light is formed on theanode 150. The organic emission layer 160 may be formed in a singlestack structure or a multi-stack structure as a stack structure foremitting white light. The organic emission layer 160 may be formed in astack structure of a fluorescent material, a phosphorescent material,and a fluorescent material, a stack structure of a phosphorescentmaterial, or a stack structure of a fluorescent material and aphosphorescent material.

The cathode 170A is formed on the organic emission layer 160. Thecathode 170A is formed in the entire region of the organic emissionlayer 160. That is, the cathode 170A is connected to a separate voltagewire to apply the same voltage to all subpixel regions, and thus is notpatterned for each subpixel region, and is formed to cover the entireregion of the organic emission layer 160.

The cathode 170A supplies an electron and thus, is formed using amaterial having a high electrical conductivity and a low work function,that is, a material for a cathode. As illustrated in FIG. 1a , when theorganic light emitting display 100 is the top emission type organiclight emitting display, the cathode 170A is formed using a significantlythin metallic material having a low work function. For example, when thecathode 170A is formed using a metallic material having a low workfunction, the cathode 170A may be formed by a metallic material such assilver (Ag), titanium (Ti), aluminum (Al), molybdenum (Mo), or an alloyof Ag and Mg at a thickness of several hundred Å or less, for example,200 Å or less, and more preferably between about 100 Å and 200 Å. Inthis case, the cathode 170A substantially corresponds to asemi-transparent layer. The light transmittance of the cathode 170A canbe decreased if the thickness is more than 200 Å, which in turn reducesthe luminance efficiency of the organic light emitting device. Also, thesurface resistance of the cathode 170A can become undesirably high ifthe thickness of the cathode 170A is less than 100 Å. Accordingly, inthe preferred embodiment, the thickness of the cathode 170A is about 150Å. In addition, the cathode 170A may be formed with carbon nanotubeand/or graphene may be used in conjunction with the metallic materialdescribed above for increased light transmittance rate and the reducedsurface resistance.

A color filter 190 is disposed on the lower substrate 110. The colorfilter 190 includes a first color filter 191, a second color filter 192,and a third color filter 193 disposed to correspond to the firstsubpixel region 110A, the second subpixel region 110B, and the thirdsubpixel region 110C. Each of the first color filter 191, the secondcolor filter 192, and the third color filter 193 is a color filter fordisplaying a predetermined color. For example, each of the first colorfilter 191, the second color filter 192, and the third color filter 193may be a color filter for displaying any one of red, green, and blue. InFIG. 1a , the first color filter 191 is defined as a red color filter,the second color filter 192 is defined as a green color filter, and thethird color filter 193 is defined as a blue color filter for convenienceof description. The fourth subpixel region 110D corresponds to the whitesubpixel region and thus, a color filter is not disposed. When whitelight emitted from an organic light emitting element disposed tocorrespond to each of the first subpixel region 110A, the secondsubpixel region 110B, and the third subpixel region 110C passes throughthe color filter 190, light having various colors may be displayed inthe organic light emitting display 100.

The upper substrate 115 is disposed on the lower substrate 110. Theupper substrate 115 is disposed to face the lower substrate 110, and maybe formed using the same material as a material of the lower substrate110.

A micro-cavity indicates that light having a predetermined wavelength isamplified by constructive interference when light is repeatedlyreflected between two layers spaced apart by an optical path length. Asillustrated in FIG. 1a , when the organic light emitting display 100 isthe top emission type organic light emitting display, the anode 150where the reflective layers 151B, 152B, 153B, and 154B, and thetransparent conductive layers 151A, 152A, 153A, and 154A are stacked isdisposed on a lower part of the organic light emitting element, and thecathode 170A including a significantly thin metallic material andcorresponding to a semi-transparent layer is disposed on an upper partof the organic light emitting element. Light emitted to the lower partof the organic light emitting element of light emitted from the organiclight emitting element is reflected on the anode 150, and travels to theupper part of the organic light emitting element. Light emitted to theupper part of the organic light emitting element and light reflected onthe anode 150 in the organic light emitting element travel to thecathode 170A. A portion thereof is discharged to the outside, and theother portion thereof is reflected to travel to the anode 150 again.Therefore, light repeatedly reflected between the anode 150 and thecathode 170A is generated, and light having a predetermined wavelengthmay be amplified by constructive interference based on a distancebetween the anode 150 and the cathode 170A, that is, a distance betweena portion where a reflection occurs on the anode 150 and a portion wherea reflection occurs on the cathode 170A. In this specification, thedistance between the anode 150 and the cathode 170A is defined as adistance between the reflective layers 151B, 152B, 153B, and 154B of theanode 150 and the cathode 170A corresponding to a semi-transparent layerfor convenience of description.

Since wavelengths of red visible light, green visible light, and bluevisible light are different from one another, different resonancedistances are set in the red subpixel region, the green subpixel region,and the blue subpixel region. A resonance distance may be set to a valuecorresponding to a multiple of a half wave length of emitted light. Whena resonance distance for light having a predetermined wavelength isformed, light having the corresponding wavelength of emitted light isrepeatedly reflected between the anode 150 and the cathode 170A, and isextracted outward with an increased amplitude due to constructiveinterference and thus, a light efficiency is enhanced. Whereas, lightnot having the corresponding wavelength has a decreased amplitude due todestructive interference when being repeatedly reflected between theanode 150 and the cathode 170A. For example, since a wavelength of redvisible light is about 650 nm, a resonance distance in the firstsubpixel region 110A corresponding to the red subpixel region may be setto a multiple of about 325 nm. Further, since a wavelength of greenvisible light is about 530 nm, a resonance distance in the secondsubpixel region 110B corresponding to the green subpixel region may beset to a multiple of about 265 nm. Further, since a wavelength of bluevisible light is about 470 nm, a resonance distance in the thirdsubpixel region 110C corresponding to the blue subpixel region may beset to a multiple of about 235 nm.

A thickness of the anode 150 positioned in each subpixel region may bedifferently adjusted to differently set the resonance distance describedabove for each subpixel region. The transparent conductive layers 151A,152A, 153A, and 154A of the anode 150, and the organic emission layer160 are positioned between the reflective layers 151B, 152B, 153B, and154B corresponding to a portion where a reflection mainly occurs on theanode 150, and a lower surface of the cathode 170A corresponding to aportion where a reflection mainly occurs on the cathode 170A. Herein, athickness of the organic emission layer 160 emitting white light is thesame in all subpixel regions. Thus, thicknesses of the transparentconductive layers 151A, 152A, 153A, and 154A of the anode 150 positionedin the respective subpixel regions may be set to different values to seta distance between the anode 150 and the cathode 170A differently foreach subpixel region. Specifically, since a resonance distance in thefirst subpixel region 110A is about 325 nm, a resonance distance in thesecond subpixel region 110B is about 265 nm, and a resonance distance inthe third subpixel region 110C is about 235 nm, a thickness of thetransparent conductive layer 151A of the first anode 151 positioned inthe first subpixel region 110A may be greater than a thickness of thetransparent conductive layer 152A of the second anode 152 positioned inthe second subpixel region 110B, and a thickness of the transparentconductive layer 152A of the second anode 152 positioned in the secondsubpixel region 110B may be greater than a thickness of the transparentconductive layer 153A of the third anode 153 positioned in the thirdsubpixel region 110C. That is, as illustrated in FIG. 1a , whenthicknesses of the reflective layers 151B, 152B, and 153B disposed inthe first anode 151, the second anode 152, and the third anode 153,respectively, are the same, thicknesses of the first anode 151, thesecond anode 152, and the third anode 153 may be set by differentlysetting thicknesses of the transparent conductive layers 151A, 152A, and153A disposed in the first anode 151, the second anode 152, and thethird anode 153, respectively.

The fourth subpixel region 110D is a white subpixel region, and is aregion in which the color filter 190 is not formed unlike the firstsubpixel region 110A, the second subpixel region 110B, and the thirdsubpixel region 110C. Thus, a micro-cavity may not be formed in thefourth subpixel region 110D. When a micro-cavity is formed, white lightemitted from the organic emission layer 160 corresponds to a colorexpressed by light having a predetermined wavelength undergoingconstructive interference by the micro-cavity, and a color shift mayoccur. However, since a metal layer is used as the cathode 170A todecrease a work function of the cathode 170A even though the metal layeris significantly thin, the cathode 170A functions as a semi-transparentlayer. Further, since the cathode 170A is formed over the entire surfaceof the organic emission layer 160, the micro-cavity is generated by thecathode 170A functioning as a semi-transparent layer in the fourthsubpixel region 110D. In addition, even when the cathode 170A issignificantly thinly formed, for example, a thickness of the cathode170A is set to about 150 A to increase a light transmittance of thecathode 170A, a reduction in power consumption and an enhancement of aluminance by the fourth subpixel region 110D may be small since a lighttransmittance of the cathode 170A is merely about 30% to 50%. Therefore,it is significantly difficult to form a micro-cavity in the red subpixelregion, the green subpixel region, and the blue subpixel region byadditionally forming the white subpixel region in the top emission typeorganic light emitting display.

In the organic light emitting display 100 according to embodiments ofthe invention, the cathode 170A formed on the organic emission layer 160includes a first region 171A having a first light transmittance and asecond region 172A having a second light transmittance greater than thefirst light transmittance. Herein, a light transmittance is a valueindicating a degree at which a predetermined material transmits light,refers to an average transmittance for each wavelength in a visiblelight wavelength region, and may be measured in various schemes. Thefirst region 171A of the cathode 170A is a region in which amicro-cavity is formed, corresponds to a plurality of subpixel regions,that is, the first subpixel region 110A, the second subpixel region110B, and the third subpixel region 110C, and may correspond to a regionin which the color filter 190 is disposed. In addition, the secondregion 172A of the cathode 170A is a region formed to minimizeoccurrence of a micro-cavity, corresponds to a single subpixel region,that is, the fourth subpixel region 110D, and may correspond to a regionin which the color filter 190 is not disposed.

A reflection decreasing layer 180A is formed on at least a portion ofthe cathode 170A so that the second light transmittance of the secondregion 172A of the cathode 170A is greater than the first second lighttransmittance first region 171A of the cathode 170A.

FIG. 1b is a conceptual diagram illustrating the cathode and thereflection decreasing layer of the organic light emitting displayillustrated in FIG. 1a . FIG. 1b illustrates the cathode 170A and thereflection decreasing layer 180A of the organic light emitting display100 illustrated in FIG. 1a for convenience of description.

Referring to FIGS. 1a and 1b , the reflection decreasing layer 180A isformed on the cathode 170A in at least a portion of the cathode 170A. Aportion of the cathode 170A coming into contact with the reflectiondecreasing layer 180A has a smaller reflectance when compared to aportion of the cathode 170A not coming into contact with the reflectiondecreasing layer 180A. The reflection decreasing layer 180A is formedusing a material capable of reducing the reflection of the organicemission layer generated light by the cathode 170A and reducemicro-cavity effect in the specific part of the organic light emittingdevice. For example, a material such as an organic matter and an oxidemay be used as the reflection decreasing layer 180A. In particular, apositive oxide may be used as the oxide. Specifically, molybdenum oxide(MoO₃), a silicon nitride (SiN_(x)), a silicon oxide (SiO₂), indium zincoxide (IZO), and the like may be used as the reflection decreasing layer180A. For example, the reflection decreasing layer 180A may be formed byan organic material using a mask, or may be printed using a nozzle andthe like.

A thickness of the reflection decreasing layer 180A may be greater thana thickness of the cathode 170A. The thickness of the reflectiondecreasing layer 180A may be set to a value greater than or equal toabout two times the thickness of the cathode 170A. As described above,when the thickness of the cathode 170A about 100 Å to 200 Å, thethickness of the reflection decreasing layer 180A may be set to about200 Å to 400 Å. For instance, when the cathode 170A is about 150 Å, thereflection decreasing layer 180A can be about 300 Å.

Referring to FIGS. 1a and 1b , the reflection decreasing layer 180A maybe formed in at least a portion of the cathode 170A, and the portion isthe fourth subpixel region 110D corresponding to the white subpixelregion. The reflection decreasing layer 180A is formed in at least aportion of an upper surface of the cathode 170A. As described above,since the cathode 170A functions as a semi-transparent layer in the topemission type organic light emitting display 100, a light transmittanceof the cathode 170A is merely about 30% to 50% in the white subpixelregion. Therefore, a light transmittance of the cathode is needed to beenhanced by decreasing an amount of light reflected by the cathode inthe white subpixel region for reducing power consumption and enhancing aluminance, and traveling toward the anode. Thus, when the reflectiondecreasing layer 180A described above is formed in the second region172A of the cathode 170A corresponding to the fourth subpixel region110D which is the white subpixel region, a light transmittance may beincreased by decreasing a reflectance in a portion of the cathode 170Acorresponding to the fourth subpixel region 110D.

In the organic light emitting display 100 according to embodiments ofthe invention, a reflectance of the second region 172A of the cathode170A may be decreased by forming the reflection decreasing layer 180A inthe second region 172A of the cathode 170A corresponding to the fourthsubpixel region 110D which is the white subpixel region. As areflectance of the second region 172A of the cathode 170A decreases, alight transmittance of the second region 172A of the cathode 170Aincreases. Thus, an amount of light reflected on the cathode 170A, andtraveling toward the anode 150 of white light emitted from the organicemission layer 160 formed in the fourth subpixel region 110D decreases.Accordingly, it is possible to minimize a micro-cavity that may begenerated in the fourth subpixel region 110D, and minimize a color shiftof white light that may occur in the fourth subpixel region 110D.

Referring to FIG. 1a , a thickness of the fourth anode 154 positioned inthe fourth subpixel region 110D may be the same as a thickness of one ofthe first anode 151, the second anode 152, and the third anode 153. Forexample, when the thickness of the fourth anode 154 is the same as athickness of the third anode 153 as illustrated in FIG. 1a , the fourthanode 154 may be similarly formed in a process of forming the thirdanode 153. In description with reference to FIG. 1a , the first subpixelregion 110A corresponds to the red subpixel region, the second subpixelregion 110B corresponds to the green subpixel region, and the thirdsubpixel region 110C corresponds to the blue subpixel region. However, acolor of each subpixel region may be changed.

In this specification, the anode 150 is defined to include thetransparent conductive layers 151A, 152A, 153A, and 154A, and thereflective layers 151B, 152B, 153B, and 154B. However, the anode 150 mayinclude the transparent conductive layers 151A, 152A, 153A, and 154A,and the reflective layers 151B, 152B, 153B, and 154B may correspond to aseparate configuration. Further, in this specification, the anode 150includes a transparent conductive material having a high work function,and a reflective metal layer. However, the anode 150 may be formed usinga conductive material having a high work function, and excellent in areflectance.

In several embodiments, at least a portion of the first anode 151, thesecond anode 152, and the third anode 153 may have the same thickness.As described above, thicknesses of the first anode 151, the second anode152, and the third anode 153 may be different from one another to form amicro-cavity. However, the organic light emitting display 100 may bedesigned in a configuration in which light having a predeterminedwavelength is amplified. Therefore, for example, the first anode 151 andthe second anode 152 may be formed to have the same thickness, and thethird anode 153 may be formed to have a thickness less than or greaterthan thicknesses of the first anode 151 and the second anode 152.

In this specification, the fourth anode 154 and the third anode 153 havethe same thickness for convenience of description. However, theinvention is not limited thereto, and the fourth anode 154 may have thesame thickness as a thickness of the first anode 151 or the second anode152.

FIGS. 1c to 1f are conceptual diagrams illustrating various positionsand thicknesses of a reflection decreasing layer of the organic lightemitting display illustrated in FIG. 1a . FIGS. 1c to 1f illustratecathodes 170C, 170D, 170E, and 170F, and reflection decreasing layers180C, 180D, 180E, and 180F for convenience of description. FIGS. 1c to1f have substantially the same configuration as a configuration of FIG.1b except for a position and a thickness of the reflection decreasinglayers 180C, 180D, 180E, and 180F. Thus, repeated description isomitted.

First, referring to FIG. 1c , the reflection decreasing layer 180C isformed on a lower surface of the cathode 170C corresponding to thefourth subpixel region 110D which is the white subpixel region. Thereflection decreasing layer 180C may be formed on the lower surface ofthe cathode 170C to decrease a reflectance in a second region 172C ofthe cathode 170C corresponding to the fourth subpixel region 110D.

A thickness of the reflection decreasing layer 180C may be set to athickness enabling an electron supplied from the cathode 170A to move toan organic emission layer. When the reflection decreasing layer 180C isformed on the lower surface of the cathode 170C to decrease areflectance in the cathode 170C, an electron from the cathode 170C maynot smoothly move to the organic emission layer due to the reflectiondecreasing layer 180C. Thus, it is possible to allow an electron to movefrom the cathode 170C to the organic emission layer by forming thereflection decreasing layer 180C to have a thickness less than or equalto about 400 Å.

Subsequently, referring to FIG. 1d , the reflection decreasing layer180D includes a lower reflection decreasing layer 181D formed on atleast a portion of a lower surface of the cathode 170D, and an upperreflection decreasing layer 182D formed on at least a portion of anupper surface of the cathode 170D. The portion of the cathode 170Ddescribed above corresponds to a second region 172D excluding a firstregion 171D.

The lower reflection decreasing layer 181D and the upper reflectiondecreasing layer 182D are formed using a material that can reduce thereflection of the light from the organic emission layer by the cathode170D. For example, a material such as an organic matter and an oxide maybe used as the lower reflection decreasing layer 181D and the upperreflection decreasing layer 182D. In particular, a positive oxide may beused as the oxide. Specifically, MoO₃, SiN_(x), SiO₂, IZO, and the likemay be used as the lower reflection decreasing layer 181D and the upperreflection decreasing layer 182D. The lower reflection decreasing layer181D and the upper reflection decreasing layer 182D have the samethickness. The lower reflection decreasing layer 181D and the upperreflection decreasing layer 182D may be formed to have the samethickness of about 300 Å to 400 Å. The lower reflection decreasing layer181D and the upper reflection decreasing layer 182D may be formed on theupper surface and the lower surface of the cathode 170D to decrease areflectance of the second region 172D of the cathode 170D.

Subsequently, referring to FIG. 1e , thicknesses of a lower reflectiondecreasing layer 181E and an upper reflection decreasing layer 182E aredifferent from each other, and the thickness of the lower reflectiondecreasing layer 181E is greater than the thickness of the upperreflection decreasing layer 182E. The lower reflection decreasing layer181E and the upper reflection decreasing layer 182E may be formed tohave a thickness of about 300 Å to 400 Å. FIG. 1e illustrates that thethickness of the lower reflection decreasing layer 181E is greater thanthe thickness of the upper reflection decreasing layer 182E. However,the thickness of the lower reflection decreasing layer 181E may be lessthan the thickness of the upper reflection decreasing layer 182E.

Subsequently, referring to FIG. 1f , a lower reflection decreasing layer181F is formed on the entire lower surface including at least a portionof a cathode 170F, and an upper reflection decreasing layer 182F isformed on an upper surface of at least a portion of the cathode 170F.For example, the lower reflection decreasing layer 181F may be formed onlower surfaces of a first region 171F and a second region 172F of thecathode, and the upper reflection decreasing layer 182F may be formed onan upper surface of the second region 172F of the cathode, that is, afourth subpixel region 110D corresponding to a white subpixel region.

FIGS. 2a and 2b are graphs illustrating a light transmittance of anorganic light emitting display according to various embodiments of theinvention.

In the graph illustrated in FIG. 2a , an x-axis corresponds to awavelength, a y-axis corresponds to a transmittance, a unit of awavelength is nm, and a transmittance is a percentage value. A curve ofa solid line in the graph illustrated in FIG. 2a depicts a lighttransmittance with respect to a wavelength when a cathode is formedusing Ag having a thickness of 150 Å, and a curve of a dotted line inthe graph illustrated in FIG. 2a depicts a light transmittance withrespect to a wavelength when a cathode is formed using Ag having athickness of 150 Å, and IZO corresponding to a positive oxide having athickness of 300 Å is formed on a surface of the cathode.

In the graph illustrated in FIG. 2b , an x-axis corresponds to awavelength, a y-axis corresponds to a transmittance, a unit of awavelength is nm, and a transmittance is a percentage value. A curve ofa thin solid line in the graph illustrated in FIG. 2b depicts a lighttransmittance with respect to a wavelength when a cathode is formedusing Ag having a thickness of 150 Å, a curve of a dotted line in thegraph illustrated in FIG. 2b depicts a light transmittance with respectto a wavelength when a cathode is formed using Ag having a thickness of150 Å, and MoO₃ having a thickness of 400 Å is formed on an uppersurface and a lower surface of the cathode, a curve of a two dotted linein the graph illustrated in FIG. 2b depicts a light transmittance withrespect to a wavelength when a cathode is formed using Ag having athickness of 150 Å, MoO₃ having a thickness of 400 Å is formed on alower surface of the cathode, and IZO having a thickness of 400 Å isformed on an upper surface of the cathode, a curve of a dashed line inthe graph illustrated in FIG. 2b depicts a light transmittance withrespect to a wavelength when a cathode is formed using Ag having athickness of 150 Å, copper phthalocyanine (CuPc) having a thickness of400 Å is formed on a lower surface of the cathode, and IZO having athickness of 400 Å is formed on an upper surface of the cathode, and acurve of a thick solid line in the graph illustrated in FIG. 2b depictsa light transmittance with respect to a wavelength when a cathode isformed using Ag having a thickness of 150 Å, CuPc having a thickness of400 Å is formed on a lower surface of the cathode, and IZO having athickness of 300 Å is formed on an upper surface of the cathode.

First, referring to FIG. 2a , when a light transmittance of a cathodewithout a separate reflection decreasing layer is measured (the solidline in the graph of FIG. 2a ), a light transmittance of about 30% to50% on average was measured. Whereas, when IZO is formed as a reflectiondecreasing layer on a surface of the cathode, and a light transmittanceis measured (the dotted line in the graph of FIG. 2a ), a lighttransmittance of about 60% to 80% on average was measured.

Subsequently, referring to FIG. 2b , when a light transmittance of acathode without a separate reflection decreasing layer is measured (thethin solid line in the graph of FIG. 2b ), a light transmittance ofabout 30% to 50% on average was measured. Whereas, in various cases inwhich a reflection decreasing layer is formed on both surfaces of thecathode, and a light transmittance is measured (the dotted line, the twodotted line, the dashed line, and the thick solid line in the graph ofFIG. 2b ), a light transmittance of about 60% to 80% on average wasmeasured.

FIG. 3a is a cross-sectional view of an organic light emitting displayincluding a cathode that includes a plurality of electrodes according toembodiments of the invention. FIG. 3a has substantially the sameconfiguration as a configuration of FIG. 1a except that a cathode 370includes a second electrode 373 and a third electrode 374. Thus,repeated description is omitted.

An organic light emitting element includes anodes 351, 352, 353, and354, an organic emission layer 360, and the cathode 370. In thisspecification, the anodes 351, 352, 353, and 354 are defined as a firstelectrode.

The second electrode 373 and the third electrode 374 are formed on theorganic emission layer 360. The second electrode 373 is formed at aposition corresponding to a first subpixel region 310A, a secondsubpixel region 310B, and a third subpixel region 310C in which a colorfilter 390 is formed, the third electrode 374 is formed at a positioncorresponding to a fourth subpixel region 310D in which the color filter390 is not formed, and the second electrode 373 and the third electrode374 are formed on the same plane on the organic emission layer 360. Thesecond electrode 373 and the third electrode 374 are electricallyconnected to each other to form the cathode 370.

The second electrode 373 is formed using a material included in thecathode 370 and having a high electrical conductivity and a low workfunction, that is, a material for a cathode. As illustrated in FIG. 3a ,when an organic light emitting display 300 is the top emission typeorganic light emitting display, the cathode may be formed using asignificantly thin metallic material having a low work function. Forexample, when the second electrode 373 is formed using a metallicmaterial having a low work function, the second electrode 373 may beformed by a metallic material such as Ag, Ti, Al, Mo, or an alloy of Agand Mg at a thickness of several hundred Å or less, for example, 150 Åor less. Thus, the second electrode 373 functions as a semi-transparentlayer.

The third electrode 374 is formed using a material included in thecathode 370 and having a high electrical conductivity and a low workfunction, that is, a material for a cathode. The third electrode 374 maybe formed using a conductive material having a low work function, andhaving a high light transmittance when compared to the second electrode373. Thus, the third electrode 374 may function as a transparent layer,or function as a semi-transparent layer having a higher lighttransmittance when compared to the second electrode 373.

A light transmittance of the second electrode 373 is different from alight transmittance of the third electrode 374. The third electrode 374may include a transparent conductive material, or function as asemi-transparent layer having a higher light transmittance than a lighttransmittance of the second electrode 373 and thus, a lighttransmittance of the third electrode 374 may be greater than a lighttransmittance of the second electrode 373. Therefore, a lighttransmittance of a white subpixel region may be increased while forminga micro-cavity in a red subpixel region, a green subpixel region, and ablue subpixel region.

In several embodiments, the third electrode 374 may be formed in aportion of the fourth subpixel region 310D, and the second electrode 373may be formed in a region in which the third electrode 374 is not formedamong the first subpixel region 310A, the second subpixel region 310B,the third subpixel region 310C, and the fourth subpixel region 310D.Thus, a light transmittance of the fourth subpixel region 310D may begreater than a light transmittance of the first subpixel region 310A,the second subpixel region 310B, and the third subpixel region 310C.

FIG. 3b is a conceptual diagram describing the organic light emittingdisplay illustrated in FIG. 3 a.

Referring to FIG. 3b , a pad part 381 for an electric connection to aflexible circuit board 380 on which a chip and a circuit transferringvarious signals from the outside to a display are mounted is formed on alower substrate 310, and a wire 382 for transferring various signalsfrom the flexible circuit board 380 is formed on the lower substrate310. Since both the second electrode 373 and the third electrode 374 areelectrodes included in the cathode 370, the second electrode 373 and thethird electrode 374 may be connected to the pad part 381, and the samevoltage may be applied to the second electrode 373 and the thirdelectrode 374 from the pad part 381.

FIG. 4 is a flowchart illustrating a method of manufacturing the organiclight emitting display according to embodiments of the invention.

First, an anode is formed on a lower substrate in S40, and an organicemission layer is formed on the anode in S41. Forming of the anode, andforming of the organic emission layer are substantially the same asforming of the anode and the organic emission layer of FIGS. 1 to 3.Thus, repeated description is omitted.

Subsequently, a cathode including a first region having a first lighttransmittance and a second region having a second light transmittancegreater than the first light transmittance is formed on the organicemission layer in S42.

Forming of the cathode may include forming a metal electrode includingmetal in the first region and the second region, and forming areflection decreasing layer having a different optical property from anoptical property of the metal electrode on a surface of the metalelectrode corresponding to the second region.

Forming of the cathode may include forming a metal electrode includingmetal in the first region, and forming a transparent electrode includinga transparent conductive material in the second region.

Hereinafter, various characteristics of the organic light emittingdevice using a reflection decreasing layer to decrease a reflectance ofa cathode with respect to light emitted from an organic emission layeraccording to an embodiment of the invention will be described.

According to another characteristic of the present invention, the anodehas a different thickness in the red, green and blue subpixel regions.

According to still another characteristic of the present invention, theanode in the white sub pixel region has substantially the same thicknessas the anode in one of the red, green and blue subpixel regions.

According to still another characteristic of the present invention, thereflection decreasing layer is formed on an upper surface, a lowersurface, or both the upper and lower surfaces of the part of the cathodecorresponding to the white subpixel region.

According to still another characteristic of the present invention, thereflection decreasing layer includes one or more of molybdenum oxide(MoO₃), a silicon nitride (SiN_(x)), a silicon oxide (SiO₂) and indiumzinc oxide (IZO).

According to still another characteristic of the present invention, thereflection decreasing layer includes an organic material.

According to still another characteristic of the present invention,wherein the anode includes a reflective metal layer and a transparentconductive oxide layer.

According to still another characteristic of the present invention, athickness of the reflection decreasing layer is greater than a thicknessof the cathode.

According to still another characteristic of the present invention, thecathode is formed of Ag with a thickness of about 100 Å to 200 Å, andwherein the reflection decreasing layer is formed of IZO with athickness of about 200 Å to 400 Å.

According to still another characteristic of the present invention, thecathode is formed of Ag with a thickness of about 100 Å to 200 Å, andwherein the reflection decreasing layer is formed of MoO₃ with athickness of about 200 Å to 400 Å.

According to still another characteristic of the present invention,wherein a first reflection decreasing layer is formed on an uppersurface and a second reflection decreasing layer is formed on a lowersurface of the cathode corresponding to the white subpixel region, thefirst and second reflection decreasing layers having a differentthickness from each other.

Hereinafter, various characteristics of the organic light emittingdevice including a plurality of cathodes having different lighttransmittances according to an embodiment of the invention will bedescribed.

According to another characteristic of the present invention, the firstpart of the organic emission layer corresponds to at least one of a redsubpixel region, a green subpixel region and a blue subpixel region, andwherein the second part of the organic emission layer corresponds to awhite subpixel region.

According to still another characteristic of the present invention, thesecond electrode and the third electrode are formed on the same plane.

According to still another characteristic of the present invention, thesecond electrode and the third electrode are electrically connected toeach other to form a cathode.

According to still another characteristic of the present invention, thesecond electrode is formed of a metal alloy, and wherein the thirdelectrode is formed of a transparent conductive oxide material.

According to still another characteristic of the present invention, thesecond electrode is formed of MgAg and the third electrode is formed ofIZO.

Hereinafter, various characteristics of a method of manufacturing theorganic light emitting device according to an embodiment of theinvention will be described.

According to another characteristic of the present invention, the stepfor forming a cathode and a reflection decreasing layer comprisesforming a first reflection reduction layer on the organic emission layercorresponding to the second part of the organic light emitting deviceand forming the cathode on the organic emission layer and the reflectiondecreasing layer.

According to still another characteristic of the present invention, themethod comprises forming a second reflection decreasing layer on thecathode corresponding to the second part of the organic light emittingdevice.

The exemplary embodiments of the present invention have been describedin more detail with reference to the accompanying drawings, but thepresent invention is not limited to the exemplary embodiments. It willbe apparent to those skilled in the art that various modifications canbe made without departing from the technical sprit of the invention.Accordingly, the exemplary embodiments disclosed in the presentinvention are used not to limit but to describe the technical spirit ofthe present invention, and the technical spirit of the present inventionis not limited to the exemplary embodiments. Therefore, the exemplaryembodiments described above are considered in all respects to beillustrative and not restrictive. The protection scope of the presentinvention must be interpreted by the appended claims and it should beinterpreted that all technical spirits within a scope equivalent theretoare included in the appended claims of the present invention.

The invention claimed is:
 1. An organic light emitting device with red,green, blue and white subpixel regions, comprising: a lower substrate;an anode formed on the lower substrate; an organic emission layer formedon the anode, the organic emission layer emitting white light; a cathodeformed on the organic emission layer; and a reflection decreasing layerformed on a part of the cathode corresponding to the white subpixelregion for reducing reflection of the light emitted from the organicemission layer by the cathode at the white subpixel region, wherein thereflection decreasing layer includes a first reflection decreasing layerand a second reflection decreasing layer, and wherein the firstreflection decreasing layer is formed on an upper surface of the cathodeand the second reflection decreasing layer is formed on a lower surfaceof the cathode corresponding to the white subpixel region.
 2. Theorganic light emitting device according to claim 1, wherein the anode inthe white subpixel region has substantially the same thickness as theanode in one of the red, green and blue subpixel regions.
 3. The organiclight emitting device according to claim 1, wherein the reflectiondecreasing layer includes one or more of molybdenum oxide (MoO3), asilicon nitride (SiNx), a silicon oxide (SiO2) and indium zinc oxide(IZO).
 4. The organic light emitting device according to claim 1,wherein the reflection decreasing layer includes an organic material. 5.The organic light emitting device according to claim 1, wherein theanode includes a reflective metal layer and a transparent conductiveoxide layer.
 6. The organic light emitting device according to claim 5,wherein a thickness of the reflection decreasing layer is greater than athickness of the cathode.
 7. The organic light emitting device accordingto claim 6, wherein the cathode is formed of Ag with a thickness ofabout 100 Å to 200 Å, and wherein the reflection decreasing layer isformed of IZO with a thickness of about 200 Å to 400 Å.
 8. The organiclight emitting device according to claim 6, wherein the cathode isformed of Ag with a thickness of about 100 Å to 200 Å, and wherein thereflection decreasing layer is formed of MoO3 with a thickness of about200 Å to 400 Å.
 9. The organic light emitting device according to claim1, wherein the first and second reflection decreasing layers have adifferent thickness from each other.
 10. A top emission type of organiclight emitting device with red, green, blue and white subpixel regions,comprising: a substrate comprising a thin film transistor (TFT) in eachsubpixel region; an anode on the substrate; an organic emission layer onthe anode, the organic emission layer emitting white light; a cathode onthe organic emission layer; and a reflection decreasing layer on a partof the cathode corresponding to the white subpixel region for increasinga light transmittance of the cathode at the white subpixel region,wherein the reflection decreasing layer includes a first reflectiondecreasing layer and a second reflection decreasing layer, and whereinthe first reflection decreasing layer is formed on an upper surface ofthe cathode and the second reflection decreasing layer is formed on alower surface of the cathode corresponding to the white subpixel region.11. A top emission type of organic light emitting device according toclaim 10, wherein the reflection decreasing layer is configured toreduce reflection of the white light emitted from the organic emissionlayer by the part of the cathode.
 12. A top emission type of organiclight emitting device according to claim 10, wherein the reflectiondecreasing layer is configured to minimize occurrence of a micro-cavitybetween the anode and the cathode correspond to the white subpixelregion.
 13. A top emission type of organic light emitting deviceaccording to claim 10, wherein the cathode is a semi-transparent layerfor emitting the white light emitted from the organic emission layer tothe top surface of the cathode.
 14. A top emission type of organic lightemitting device according to claim 10, wherein the organic emissionlayer is configured to emit the white light to the cathode.